1. Field of the Invention
The invention relates to a charging control apparatus and a charging control method for a battery.
2. Description of Related Art
In an electric vehicle, regenerative braking force is used to apply a brake to a drive wheel connected to a motor that is driven by a battery. At this time, power generated by the motor as a result of the regenerative braking is charged to a battery and thereby collected. When the battery is charged beyond a limit, however, the battery enters an overcharged state. To suppress such situations, a battery charging control apparatus that compares a battery voltage to a battery voltage limit and controls charging of the battery to ensure that the battery voltage does not exceed the battery voltage limit has been proposed (Japanese Patent Application Publication No. 6-153314 (JP 6-153314 A), for example).
A lithium ion secondary battery has a high energy density and both a higher initial open circuit voltage and a higher average operating voltage than other secondary batteries. A lithium ion secondary battery is therefore suitable for use in a power supply system for a hybrid automobile or the like that requires a large battery capacity and a high voltage. Further, a coulombic efficiency of a lithium ion secondary battery is close to 100%, and therefore the battery exhibits superior charging/discharging efficiency. Accordingly, the energy of a lithium ion secondary battery can be used more effectively than that of other secondary batteries.
However, depending on the manner in which the lithium ion secondary battery is used (for example, charging at a high rate, charging from a high state of charge (SOC), long-term continuous charging, or charging at a low temperature (charging in a state of high resistance)), lithium (Li) metal may be deposited on a negative electrode surface of the lithium ion secondary battery, and as a result, overheating or performance deterioration may occur in the lithium ion secondary battery.
It is therefore desirable to suppress lithium metal deposition in the negative electrode. Lithium metal deposition can be suppressed by greatly limiting a charging amount. In this case, however, it is impossible to collect a sufficient amount of the power generated by regenerative braking. Further, when the battery is charged by an external power supply, charging takes a long time.